1. The Field of the Invention
This invention relates to apparatus and methods for measuring body composition using bioelectrical impedance analysis (BIA). More particularly, the present invention relates to apparatus and methods for determining body fat, lean body mass, body fluid, and other physiological parameters using bioelectrical impedance analysis.
2. The Prior Art
It is widely recognized that many people can greatly benefit from having a knowledge of their body composition, i.e., what portion of their body comprises fat, lean mass, body fluids, and so forth. For example, athletes need to know their body composition to customize their training regimen. Also, patients can be better treated by a physician if their body composition is known. Furthermore, people who are overweight can benefit from knowing their body composition, especially as they set weight reduction goals.
The importance of body composition is gaining extensive recognition. It is now realized that excess body fat in humans may cause, or at least contribute to, heart attacks, diabetes, hypertension, atherosclerosis, gallbladder disease, osteoarthritis, certain types of cancer, and even premature death. Thus, it is desirable to know what proportion of a person's weight is attributable to fat and other biological components.
The most widely accepted technique for determining what proportion of a person's body mass is attributable to fat is hydrostatic weighing or, in other words, weighing underwater. Since fat, muscle, bone, fluid, and other body components each have a known specific density, hydrostatic weighing allows the proportion of fat in comparison to these other body components to be estimated. While accepted as the "standard" technique for determining total body fat, hydrostatic weighing is also very inconvenient for the subject.
In order to provide more convenient body fat determinations, other techniques have been used. One of the techniques which has been used in the past employs calipers to measure the thickness of one or more skin folds on a body. While the measurement of skin folds is very convenient, it is also inaccurate in many cases. While other techniques have been proposed which are more convenient than hydrostatic weighing, such as isotope dilution, imaging methods, and measurement of fat soluble gases distributed throughout the body, one technique which has received widespread recognition is the measurement of a body's resistance to the flow of electrical current to determine the proportion of fat in the body. More precisely, the measurement of bioelectrical impedance (Z), which includes the electrical parameters of resistance, reactance, and reluctance, is often used to determine the proportion of body fat for a particular subject.
Previously available techniques and apparatus for measuring body fat and other biological components using bioelectrical impedance are exemplified in U.S. Pat. Nos. 4,895,163 and 4,911,175. Such previously available techniques and apparatus generally share several disadvantageous characteristics. Among such characteristics is that the whole body is treated as a single, lumped conductor not accounting for differences in electrical characteristics of each body segment. Also, the previously available techniques and apparatus assume that once the total body impedance is determined, the body composition of all subjects can be obtained by fitting the total body impedance to a predetermined profile. Due to significant differences between individual subjects, however, there is a substantial portion of the population for which the prior techniques provide inaccurate results. In an effort to improve their accuracy, some previously available techniques also consider parameters such as the height, weight, gender, age, and activity level of the subject in addition to the total measured body impedance.
Significantly, while the previous body impedance analysis techniques work for some of the general population, it has generally been unrecognized in the art that the prior techniques do not provide accurate body fat calculations for a significant portion of the population.
In view of the foregoing, it would be a significant advance in the art to provide an improved method and apparatus for measuring body composition by bioelectrical impedance.